The present invention relates to an electrode and method for measuring muscle activity in the pharyngeal airways and, in particular, to diagnosing sleep apnea in wakeful patients.
An estimated 2% to 4% of the population are believed to suffer from sleep apnea syndrome. Sleep apnea is a condition that results from a reduction in air intake through the air passage of sleeping individuals. This problem arises as a result of weak muscle tone in the throat and although compensated for during waking hours, gives rise to symptoms of fatigue during the day, poor quality sleep at night, and heavy snoring during sleep. Diagnosis of sleep apnea has been carried out in sleep laboratories where the patient is monitored at night during sleep in a process called nocturnal polysomnography. This diagnostic test is expensive, time consuming, and must be administered by highly trained technicians. Consequently, availability of the test is limited.
The monitoring of sleep apnea traditionally took the form of electromyographic (EMG) analyses of the genioglossus muscle. The analysis relied on intramuscular electrode recordings which were made by inserting a needle or wire electrode into the body of the muscle just below the teeth. With the needle electrodes it is not possible to make quantative comparisons to the EMG recordings if the electrode is moved or replaced because the tip of the needle cannot be placed at exactly the same position within the muscle. Consequently, the needle electrodes measure activities from different anatomical and architectural organizations and different fiber types.
An alternative approach was suggested by Doble et al. in J. Applied Physiology 58 (4): 1378-82 (1985). This approach employed an intra-oral surface recording electrode for monitoring the genioglossus EMG activity. A mouth electrode was fitted to the teeth in order to make quantitative measurements of EMG activity. Doble""s mouthpiece electrode was bulky and interfered with the action of the tongue. Under Doble""s approach, patients were seated in a dental chair with their neck flexed forward at an angle of 30 degrees and were required to maintain this head position during the tests.
Takada et al., J. Dent. Res. 75: 1598-1606 (1996), conducted further studies to examine tongue, jaw and lip muscle activity utilizing an electrode assembly that relied on fixation to the teeth.
The present invention provides an electrode, apparatus and method for measuring muscle activity in the pharyngeal airways and sleep apnea while the subject is awake. The invention is convenient and increases availability of testing to patients. The invention also reduces the cost of diagnosis.
In a preferred embodiment of the invention, an electrode is provided for measuring muscle activity in the pharyngeal airways, comprising: an electrode body for placement in a human mouth, the body having a face defining a plane, and at least one leg extending from the face, the leg having an electrical contact such that when the electrode body is placed in the mouth, the contact is in communication with the genioglossus muscle.
The body is preferably formed from a biologically inert material. In a further embodiment, the at least one leg is between 2 mm and 8 mm in length. In another preferred embodiment, the at least one leg extends from the face at a substantially 90 degrees. The body also preferably has four legs, the four legs each extending from the face at substantially 90 degrees angles such that the legs form the vertices of a square.
In a preferred embodiment, the body of the electrode has at least two legs and is bifurcated such that each part of the body has one leg which can be placed on each side of a frenum in a human mouth. In yet another embodiment, the electrode body is formed into a crescent contour.
In another preferred embodiment, a method is provided for measuring muscle activity in the pharyngeal airways comprising: placing an electrode having an electrode body in a mouth, the body having at least one electrical contact such that when the electrode body is placed in the mouth, the contact is in communication with the genioglossus muscle; recording signals received from the electrode; and comparing the signals to signals obtained from normal pharyngeal muscle activity. To diagnose sleep apnea, the signals are compared to signals obtained from people without sleep apnea.
In a further embodiment, a method is provided for diagnosing sleep apnea wherein the signals are compared to signals taken from the same patient at a different session and further comprising: amplifying the signals; filtering the signals; integrating the signals; and feeding the results into a computer for analysis.
In another preferred embodiment, an apparatus for diagnosing sleep apnea is provided comprising: an electrode having an electrode body for placement in a patient""s mouth, the body having at least one electrical contact such that, when the electrode body is placed in the mouth, the contact is in communication with the genioglossus muscle; an amplifier in electrical communication with the electrode to receive EMG signals from the electrode; a signal filter in electrical communication with the amplifier; a rectifier in electrical communication with the filter such that the rectifier receives the filtered signal; and a signal integrater in electrical communication with the rectifier whereby the rectified signal is integrated on a moving time average basis.